Inside the extruder: making kibble
By the time dry dog food is packaged, the transformation of living tissue and whole plants into a commercial commodity is complete. The original ingredients are milled, hydrated, thermally processed, mechanically altered, expanded, dehydrated and coated. Each stage alters the physical structure of the food and, with it, the form and behaviour of its nutrients. The molecular matrix undergoes a combination of transformations, alterations, and dismantling (fragmentation); native food matrices are destroyed in a process designed to produce a shelf-stable, uniform and cost-effective product at scale (context: dry pet food will account for a 68% share in a market worth 134.46 billion dollars in 2026)[1].
These harsh processes drastically alter – artificialise – the food matrix, prompting broader questions in modern food science:
What happened to the food’s structure?
How were nutrients and bioactive compounds altered?
What was gained?
What was lost?
What new compounds were created?
What trade-offs occurred?
The extrusion process is brutal.
This is the reality of the kibble manufacturing processes.
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Particle size and mixing
Animal and plant-derived ingredients are milled and blended into a homogeneous mix. Milling, where “intact tissues” and plant structures are ground into suitably sized particles, disrupts cellular integrity and reduces structural heterogeneity. The starting mix for extrusion is already a physically altered material.
Assuming, of course, that any of the “tissues” involved are still intact: some – if not all – ingredients entering the mix will already have been processed out of recognition. Take “chicken meal”: consumers seeing this on a label might imagine a flour-like substance, a whole food ground down like flaxseed meal or almond meal. But they would be wrong. This ‘meal’ is the output of industrial rendering. This high-temperature process reduces animal tissues like muscle, skin, connective tissue and bone – from animals unsuitable for human consumption – to a dry, concentrated ingredient. But because the product isn’t for human consumption, this process falls outside the scope of the NOVA classification system. [2]
Let’s think about that for a moment. Putting pre-rendered meat through a second thermal process is, in effect, ultra-processing squared. This practice is standard in the pet industry – so standard that it has a name: sequential or secondary processing. But “ultra-ultra-processing” better captures the reality.
This is a point of significant divergence between economy and premium formulations: the raw inputs. Premium formulations typically use fresh, unrendered tissues, preserving structure prior to the first thermal processing. Economy foods are more likely to rely on pre-processed, rendered animal meals.
Conditioning
Having destroyed the physical matrix, the process goes on to transform the remaining molecular matrix. Steam and water hydrate and soften the mixture, bringing the remaining separate particles into a cohesive slurry. Moisture swells starch granules and untangles protein strands, facilitating a more uniform heat transfer during the extrusion process ahead.
In the extruder barrel
Once fully hydrated, the slurry is pumped into an extruder barrel. In a process known as shearing, one or two rotating screws (twin screws for higher meat content, single screw for grain-based recipes[3]) force layers of thick slurry to slide past each other in opposite directions, dragging and stretching the mixture with great force to form a dough.
Heat, pressure and mechanical shear in the barrel trigger multiple molecular shifts:
- starch gelatinisation
- protein denaturation
- fibre realignment
- degradation or oxidation of native enzymes, bioactive peptides and fatty acids.
- the Maillard reaction produces a range of compounds that add colour and flavour
- essential amino acids, particularly lysine, are less available for absorption.
By the end of the process, the multiple, complex matrices of the original whole foods have collapsed entirely, then been rebuilt into a single, engineered matrix.
Die exit, expansion and dehydration
At this point, the material exits the die. A sudden pressure drop causes superheated water to vaporise, expanding the mass into a porous kibble and locking in its shape. The extruded shapes are dried immediately, so as to inhibit microbial growth and provide shelf stability. The resulting product: a new, dry matrix.
The supplementation paradox
Lastly, the dried and cooled product enters the finishing stage for what are known, ironically enough, as post-kill additions. (Except, to be clear, the “kill” here doesn’t refer to the destruction of vitamins, enzymes and nutrients as you might think. It’s about reducing pathogens.)
And bizarrely, the final nutritional profile is determined more by these post-processing additions than the inherent quality of the product’s ingredients. Many of these synthetic premixes are sensitive to oxygen, light and heat, and can start to degrade once the product is exposed to air.
Industrially produced chemical additives and synthetic vitamins – in other words more UPFs – compensate for the loss and degradation of native compounds and food matrices, re-fortify the product and render it compliant with established nutritional standards. This might meet recommended requirements, but does not, and cannot, replicate the structural context in which nutrients naturally occur and interact with other compounds to influence stability, absorption and function. Fats and oils are sprayed on to restore energy density and add flavour.
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In the bag
Extrusion is an old industrial technology, used in pet food since the mid 20th century. It has remained a stalwart in an evolving industry, withstanding trends like premiumisation and humanisation.
And that’s important to remember when we choose our dog’s food – because whatever message the brightly coloured images convey, the extruded product has stayed the same, constrained by the unchanging physics of the extruder.
References:
[1] Fortune Business Insights Pet Food Market Size, Share & Industry Analysis and Regional Forecast, 2026–2034 Last Updated: June 15, 2026 Report ID: FBI100554
[2] Davidou S, Christodoulou A, Frank K, Fardet A, A study of ultra-processing marker profiles in 22,028 packaged ultra-processed foods using the Siga classification, Journal of Food Composition and Analysis, Volume 99, 2021, 103848, ISSN 0889-1575, https://doi.org/10.1016/j.jfca.2021.103848.https://www.sciencedirect.com/science/article/abs/pii/S088915752100048X
[3] https://loyal-foodmachine.com/pet-food-extrusion-process/